1. Field of the Invention
This invention relates generally to oilfield operations and more particularly to systems and methods utilizing fiber optics for monitoring wellbore parameters, formation parameters, drilling operations, condition of downhole tools installed in the wellbores or used for drilling such wellbores, for monitoring reservoirs and for monitoring of remedial work.
2. Background of the Art
A variety of techniques have been utilized for monitoring reservoir conditions, estimation and quantities of hydrocarbons (oil and gas) in earth formations, for determination formation and wellbore parameters and form determining the operating or physical condition of downhole tools.
Reservoir monitoring typically involves determining certain downhole parameters in producing wellbores, such as temperature and pressure placed at various locations in the producing wellbore, frequently over extended time periods. Wireline tools are most commonly utilized to obtain such measurements, which involves shutting down the production for extended time periods to determine pressure and temperature gradients over time.
Seismic methods wherein a plurality of sensors are placed on the earth""s surface and a source placed at the surface or downhole are utilized to obtain seismic data which is then used to update prior three dimensional (3-Dxe2x80x3) seismic maps. Three dimensional maps updated over time are sometimes referred to as xe2x80x9c4-Dxe2x80x9d seismic maps. The 4-D maps provide useful information about reservoirs and subsurface structure. These seismic methods are very expensive. The wireline methods are utilized at great time intervals, thereby not providing continuous information about the wellbore conditions or that of the surrounding formations.
Permanent sensors, such as temperature sensors, pressure sensors, accelerometers or hydrophones have been placed in the wellbores to obtain continuous information for monitoring wellbores and the reservoir. Typically, a separate sensor is utilized for each type of parameter to be determined. To obtain such measurements from useful segments of each wellbore, which may contain multilateral wellbores, requires using a large number of sensors, which require a large amount of power, data acquisition equipment and relatively large amount of space, which in many cases is impractical or cost prohibitive.
In production wells, chemicals are often injected downhole to treat the producing fluids. However, it can be difficult to monitor and control such chemical injection in real time. Similarly, chemicals are typically used at the surface to treat the produced hydrocarbons (i.e. break down emulsions) and to inhibit corrosion. However, it can be difficult to monitor and control such treatment in real time.
Formation parameters are most commonly measured by measurement-while-drilling tools during the drilling of the wellbores and by wireline methods after the wellbores have been drilled. The conventional formation evaluation sensors are complex and large in size and thus require large tools. Additionally such sensors are very expensive.
Prior art is also very deficient in providing suitable system and methods for monitoring the condition or health of downhole tools. Tool conditions should be monitored during the drilling process, as the tools are deployed in the wellbore and after deployment, whether during the completion phase or the production phase.
The present invention addresses some of the above-described prior deficiencies and provides systems and methods which utilize a variety of fiber optic sensors for monitoring wellbore parameters, formation parameters, drilling operations, condition of downhole tools installed in the wellbores or used for drilling such wellbores, for monitoring reservoirs and for monitoring of remedial work. In some applications, the same sensor is configured to provide more than one measurement, in many instances these sensors are relatively, consume less power and can operate at higher temperatures than the conventional sensors.
The present invention provides fiber optics based systems and methods for monitoring downhole parameters and the condition and operation of downhole tools. The sensors may be permanently disposed downhole. The light source for the fiber optic sensors may be disposed in the wellbore or at the surface. The measurements from such sensors may be processed downhole and/or at the surface. Data may also be stored for use for processing. Certain sensors may be configured to provide multiple measurements. The measurements made by the fiber optic sensors in the present invention include temperature, pressure, flow, liquid level, displacement, vibration, rotation, acceleration, acoustic velocity, chemical species, acoustic field, electric field, radiation, pH, humidity, electrical field, magnetic field, corrosion and density.
In one system, a plurality of spaced apart fiber optic sensors are disposed in the wellbore to take the desired measurements. The light source and the processor may be disposed in the wellbore or at the surface. Two way communication between the sensors and the processor is provided via fiber optic links or by conventional methods. A single light source may be utilized in the multilateral wellbore configurations. The sensors may be permanently installed in the wellbores during the completion or production phases. The sensors preferably provide measurements of temperature, pressure and flow for monitoring the wellbore production and for performing reservoir analysis.
In another system the fiber optic sensors are deployed in a production wellbore to monitor the injection operations, fracturing and faults. Such sensors may also be utilized in the injection well. Controllers are provided to control the injection operation in response to the in-situ or real time measurements.
In another system, the fiber optic sensors are used to determine acoustic properties of the formations including acoustic velocity and travel time. These parameters are preferably compensated for the effects of temperature utilizing the downhole temperature sensor measurements. Acoustic measurements are use for cross-well tomography and for updating preexisting seismic data or maps.
The distributed sensors of this invention find particular utility in the monitoring and control of various chemicals which are injected into the well. Such chemicals are injected downhole to address a large number of known problems such as for scale inhibition and for the pretreatment of the fluid being produced. In accordance with the present invention, a chemical injection monitoring and control system includes the placement of one or more sensors downhole in the producing zone for measuring the chemical properties of the produced fluid as well as for measuring other downhole parameters of interest. These sensors are preferably fiber optic based and are formed from a sol gel matrix and provide a high temperature, reliable and relatively inexpensive indicator of the desired chemical parameter. The downhole chemical sensors may be associated with a network of distributed fiber optic sensors positioned along the wellbore for measuring pressure, temperature and/or flow. Surface and/or downhole controllers receive input from the several downhole sensors, and in response thereto, control the injection of chemicals into the brothel.
The chemical parameters are preferably measured in real time and on-line and then used to control the amount and timing of the injection of the chemicals into the wellbore or for controlling a surface chemical treatment system.
An optical spectrometer may be used downhole to determine the properties of downhole fluid. The spectrometer includes a quartz probe in contact with the fluid. Optical energy provided to the probe, preferably from a downhole source. The fluid properties such as the density, amount of oil, water, gas and solid contents affect the refraction of the light. The refracted light is analyzed to determine the fluid properties. The spectrometer may be permanently installed downhole.
The fiber optic sensors are also utilized to measure formation properties, including resistivity, formation acoustic velocity. Other measurements may include electric field, radiation and magnetic field. Such measurements may be made with sensors installed or placed in the wellbore for monitoring the desired formation parameters. Such sensors are also placed in the drill string, particularly in the bottom hole assembly to provide the desired measurements during the drilling of the wellbore.
In another system, the fiber optic sensors are used to monitor the health or physical condition and/or the operation of the downhole tools. The measurements made to monitor the tools include one or more of (a) vibration, (b) noise (c) strain (d) stress (e) displacement (f) flow rate (g) mechanical integrity (h) corrosion (i) erosion (j) scale (k) paraffin and (l) hydrate.
Examples of the more important features of the invention have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art maybe appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.